1. Field of the Invention
The present invention relates to ternary blends of an acrylate-styrene-acrylonitrile interpolymer, a poly (methyl methacrylate) resin and a polycarbonate resin which exhibit an improved combination of impact and flexural properties.
2. Description of the Prior Art
Polycarbonate resins are tough, rigid engineering thermoplastics having good impact strength. However, they have low flow characteristics which sometimes cause difficulties in processing. Various prior art attempts have been made to blend polycarbonate resins with other polymeric modifiers to solve this problem while still retaining the toughness and impact resistance of the polycarbonate resin.
Blends of a polycarbonate resin and an interpolymer of acrylate-styrene-acrylonitrile (referred to as ASA) are disclosed in U.S. Pat. No. 4,148,842 (Yu, et al.) which is incorporated herein by reference. The patent describes weather resistant blends having good processing properties while retaining the impact properties of polycarbonate.
Blends of interpolymers with acrylic polymers have been shown in EPC Patent Application No. 81-105, 711.6.
The addition of poly (methyl methacrylate) resin (referred to as PMMA) to acrylate-styrene-acrylonitrile interpolymer contributes product improvements in tensile and flexural strength and modulus, hardness and gloss.
It has now been discovered that ternary combinations of acrylate-styrene-acrylonitrile interpolymer, poly (methyl methacrylate) resin and polycarbonate resin exhibit a wide range of useful properties unavailable in binary systems. Although commercially available ASA-PMMA blends have the noteworthy properties mentioned above, these materials suffer from relatively low notched Izod strength due to the presence of the poly (methyl methacrylate). As might be expected, the addition of increasing amounts of polycarbonate will improve the notched Izod. However, increasing the ASA interpolymer content in an ASA-PMMA-PC system while holding the polycarbonate content constant will also improve the notched Izod impact.
Surprisingly, an increase in the acrylate-styrene-acrylonitrile content while holding the poly (methyl methacrylate) constant results in decreased notched Izod impact. It is also surprising that although the Gardner impact properties follow the same relationship as the notched Izod properties mentioned above, the flexural properties behave quite differently.
As an example, a high modulus was found for the ternary system having an ASA/PC/PMMA ratio of approximately 55/17.5/27.5. An increase in the acrylate-styrene-acrylonitrile interpolymer content of such a system decreases the modulus regardless of the PC/PMMA ratio.
It is thus apparent that the ternary system of the present invention provides a complicated variety of interdependent properties which can be chosen by those skilled in the art depending upon intended applications.